1. Field of the Invention
The present invention relates to a device for supplying air to the combustion chamber of a boiler furnace designed for normal operation with natural gas while utilizing forced-draft fans or blowers for delivering air to the burners as well as for temporary operation with an emergency fuel consisting of fuel oil.
When an emergency fuel is employed, devices of this type make it possible to maintain a steam-generating furnace in operation at the cost of a certain reduction of the optimum operating range.
2. Description of the Prior Art
For temporary oil-firing of a furnace combustion chamber designed for normal operation with natural gas, it has already been proposed to make use of blower-type fans for delivering air under a pressure of higher value than that required for normal operation with natural gas and corresponding to the pressure required for oil-firing while also incorporating auxiliary blowers and circuits for recycling flue gases to the combustion chamber by means of these auxiliary blowers. However, this makes it necessary to provide main blowers of unduly large size as well as to instal and maintain at least two auxiliary blowers and heat-insulated recycling ducts. Furthermore, the power consumption of both main and auxiliary blowers in emergency operation is quite considerably higher than the power consumption under normal operating conditions. The installation of these auxiliaries therefore carries a heavy penalty both in capital investment and input power requirements. Moreover, the operation of the combustion chamber is modified since the flame temperature obtained from fuel oil is lower than that of natural gas, with the result that the temperature of the combustion gases at the level of the superheaters and resuperheaters of the boiler furnace is reduced and results in less favorable heat-transfer efficiency.
The object of the present invention is to provide a supply device for temporary operation with fuel oil which does not involve any need for over-dimensioning of the main air blowers, which does not call for the installation of a flue-gas recycling circuit, and which minimizes the additional capital cost and power consumption which correspond to the possibility of emergency operation.